1. Field of the Invention
This invention relates generally to air ducts and fan-driven vents and, in particular, to air-conditioner (A/C) air ducts and fan-driven filters used, e.g., in semiconductor fabrication cleanrooms.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
Cleanrooms are often employed in applications such as semiconductor manufacturing, in environments in which it is important to minimize external contaminants such as dust or other particles. For example, cleanrooms may be employed to house equipment used to grow and process devices such as electronics, microchips, processors, and optoelectronics, on semiconductor wafer substrates.
Cleanrooms are often designated by a numerical class. For example, a class 10,000 cleanroom is one having (depending on the standard employed) a maximum of 10,000 measured 0.5 xcexcm or greater size particles in a cubic foot of air in the room. In cleanrooms, clean, filtered air is constantly pumped into the room through an air vent to maintain positive pressure in the room, so that air always blows out of the room. This function is typically performed by blower/filter modules (BFMs, or FBMs), which typically employ a filter, and a blower (fan), such as a venturi blower, to provide a vertical laminar flow of HEPA- or ULPA-filtered air. Air is taken into an air inlet on the top, and filtered air is blown out of a vent at the bottom of the BFM.
The filters employed by BFMs include HEPA (high efficiency particulate arrestance (or air)) and ULPA (ultra-low penetration air) filters. HEPA filters are typically rated 99.99% efficient at removing particles 0.3 microns in diameter or larger, while ULPA filters are typically rated 99.999% efficient at removing particles 0.12 microns in diameter or larger.
BFMs are manufactured by various vendors, including the Patriot High Purity HEPA Filter Blower model no. BFM 24 LPF, available from Airflotek, Inc., 2150 Northmont Pkwy., Suite H, Duluth Ga. 30096 (information available on the web at www address airflotek.com). Other BFMs include the American Cleanroom Systems Magnum 800 (M800) Motorized HEPA Filter, sold by Cintas Cleanroom Resources (information available on the web at www address cintas-corp.com/clean). BFMs may be employed in both conventional or softwall cleanrooms. When installed in the former, the BFM may be installed in the ceiling grid system of the cleanroom, with the air intake taking air from the plenum.
Cleanrooms also often need to be air-conditioned (A/C) to maintain the temperature and humidity levels of the room within acceptable ranges.
In a conventional cleanroom, the entire room is maintained as a cleanroom. Air is pumped into the room via vents of BFMs, typically mounted in the ceiling, to maintain positive air pressure in the room with respect to the environment outside the room. An A/C system may also be used, instead of (or in addition to) a BFM, to perform similar function. For example, the A/C duct is run to a vent to the room, via a HEPA filter, where the A/C system fan is always on; the cooling element of the A/C system is switched on and off as desired, to maintain temperature and humidity.
In a xe2x80x9cportablexe2x80x9d or softwall cleanroom, a cleanroom is erected within a larger, air-conditioned room. Such a cleanroom typically consists of a frame, with a sealed top (roof), and with clear plastic xe2x80x9ccurtainxe2x80x9d softwalls. A fan-driven filter, such as the model BFM 24 LPF described above, is typically mounted in the roof portion of the portable cleanroom. The filter constantly filters and pumps the (already air-conditioned) air in the room into the portable cleanroom, to maintain positive air pressure in the portable cleanroom with respect to the room in which it is disposed.